1. Field of the Invention
The present invention relates generally to a novel use of Rhodopseudomonas palustris DSM 29314, and more particularly to reduce nitrate content in a plant.
2. The Prior Arts
For improving yield and quality of vegetables, fertilizer management is an inalienable part of agricultural cultivation, however, the excessive use of nitrogen-containing fertilizers or harvesting vegetables at low light intensity and during early morning all contribute to higher nitrate content in the vegetables. Although nitrate itself is harmless to human body, but it has been reported that about 5% of dietary nitrate is converted to a cancer-causing nitrite. Therefore, it needs to reduce the intake of nitrate for health consideration, in 1995, Food and Agriculture Organization/World Health Organization (FAO/WHO) Joint Expert Committee on Food Additives (JECFA) has recommended that acceptable per day daily intake (ADI) of nitrate do not exceed 3.7 mg nitrate ions per kilogram body weight. Vegetables represent the main source of human intake of nitrate, the maximum levels of nitrates in vegetables, such as spinach and lettuce, are provided by European Commission according to this recommendation in 1997 (<3000 ppm or [mg/Kg fresh weight]). Consumer awareness of food safety issues is high, providing the quality, safety and wholesomeness of crops is the responsibility of agricultural producers. Effectively reducing the residual nitrate content in the vegetables can not only ensure consumers to fell more at ease with eating, but also reducing the inappropriate use of chemical fertilizers minimizing the load on the environment.
In order to reduce the nitrate content in vegetables, soil cultivation can be improved by adding soil improvement materials and avoiding harvest early in the morning, besides reducing the amount of nitrogen-containing fertilizer and selecting low nitrate accumulation of vegetables. But it is difficult to transport the vegetables harvested at late afternoon or evening from farm field to market at the same day, which results in any additional costs incurred, such as overnight storage costs, and the appearance and quality of the crops are susceptible to be damaged. Also, under indoor artificial light, there are several ways to reduce nitrate content, including increasing light intensity, changing light source, modifying the composition of the hydroponic nutrient solution or interrupting the hydroponic nutrient solution, etc. In order not to affect yield, many general ways of reducing nitrate content are to analyze the components in soil or hydroponic nutrient solution prior to cultivation, and to determine the minimum amount of nitrogen-containing fertilizer demand, then to add the nitrogen fertilizer at appropriate time for planting, however, which tends to be more labor-intensive.
In recent years, microbe-related biotechnology has been used to solve some problems in agriculture and environment; those microorganisms are generally designated as plant-growth-promoting rhizobacteria (PGPR), and mainly applied in soil growing system. It is well-known that denitrifying or nitrate reducing bacteria can precede the reduction of nitrite to NO, N2O or N2 through anaerobic respiration; however, there are numerous problems which the use of denitrifying bacteria for reducing nitrate content in agriculture can cause. These include: 1. generally, the denitrifying bacteria precedes the reduction of nitrate under anaerobic or microaerobic conditions, but plant growth is in sufficient oxygen environment; 2. the reduction of nitrate in the plant is to rely on the plant nitrate reductase, denitrifying bacteria must be endophyic bacteria; otherwise, the bacteria cannot directly precede the reduction of nitrate. People gradually demand for high quality, fresh, non-toxic and safe agriculture; therefore, it needs to provide a high quality and stability fertilizer for improving yield and quality of vegetables. That not only increases farmer's willingness to use, but also takes into account the yield and sustainable development of vegetables.